1. Field of the Invention
The invention relates to a guide crank for the cover of an openable motor vehicle roof with a crank body which is connected to the cover and which comprises at least one slotted opening, wherein the opening forms a guideway or is used as the receiver of a guide body which has the guideway.
2. Description of Related Art
One such guide crank is known, for example, from German patent applications DE 35 29 118 C2 or DE 196 23 945 C1. The guideway of the guide crank is used for movable accommodation of a crank pin of a cover actuation mechanism for swivelling and/or moving the cover in the lengthwise direction of the motor vehicle. The crank body of a generic guide crank must have sufficient stiffness and torsional resistance so that the cover does not tend to vibrate under vertical loads, as are caused among others by wind load. The crank should not plasticly deform even under an overload which occurs, for example, when the cover actuation mechanism is actuated with the cover frozen to a vehicle-mounted frame. In this case guide cranks with very long guideways are especially critical. These guide cranks are used in cover actuation mechanisms in which the crank pin is attached directly to a slide piece of a guide rail which runs in the displacement direction of the cover. However, the crank body of a guide crank with a shorter guideway is also somewhat weakened by the slotted opening. A shorter guideway is typically used when the crank pin is attached to a raising lever which is swivel mounted on the slide piece of the guide rail.
Guide cranks of the aforementioned type are therefore made frequently as a relatively thick sheet metal part which, in addition, can have bends. In particular, above or below the opening, relatively high crosspieces must remain in order to prevent plastic deformation of the guideway under load, and to minimize elastic deformation and the tendency to vibration. This results in the fact that generic guide cranks, having a guide body consisting of a sheet metal part, have considerable weight and require a large installation height. If the crank body of the guide cranks of the above mentioned type is made of plastic, it must be made thicker for reasons of strength thereby taking up even more installation height.
These fundamental disadvantages also afflict cranks with crank bodies made as a composite which, for example, has a layered structure consisting of an inner plastic body and preferably two side metal bodies as shown in German patent application DE-44 05 742 C1.